The present invention relates to an arrangement for providing engagement for a frictional clutch assembly. More specifically, the present invention relates to a limited slip feature for a clutch assembly of a roller/ramp variety which provides limited torque transfer until the clutch assembly is engaged.
Often, components of a system require selective engagement. Two such systems which are used in automotive applications are differential assemblies and transfer cases.
Differential assemblies are used in motor vehicles to allow the wheels to turn at different rotational speeds while still providing power to the wheels. Various types of differential assemblies are used in motor vehicles to redirect the transfer of power to the driving axles.
A limited slip differential assembly is a type of differential assembly which can be selectively engaged to provide positive traction to the wheels. A limited slip differential assembly typically uses clutch pads to link a differential housing to one or both side gears which results in a limited amount of torque being sent to a non-spinning wheel. Unfortunately, limited slip differentials typically have low torque capacity which, during certain high power operating conditions, can result in insufficient power being transmitted through the differential assembly. In these cases, wear of the clutch pads may occur, which adversely affects the performance of the differential assembly.
Another differential assembly design that is used to overcome the shortcomings of the standard differential assembly is known as the locking differential. A locking differential typically engages a xe2x80x9cdogxe2x80x9d clutch or an axial gear set to lock the two axle halves together. Unfortunately, locking differentials cannot be engaged xe2x80x9con-the-flyxe2x80x9d because any relative motion between the gear teeth would result in severe mechanical damage.
A transfer case is another type of automotive application that may require selective engagement of certain system components. A part-time transfer case is a device which can selectively provide power to the alternate drive wheels in a four-wheel drive vehicle. Various types of part-time transfer cases are known. Unfortunately, due to the rigorous operating conditions that part-time transfer cases are exposed to, wear often occurs in the components, resulting in a decreased level of performance in the system.
It is known in the art to selectively lock various drivetrain components using roller/ramp clutch assemblies. For example, the two-way over-running clutch assembly described in U.S. Pat. No. 5,927,456, assigned to NTN Corporation, and hereby incorporated by reference, describes a clutch assembly of a roller ramp variety and the mechanism by which the rollers are retained and biased in the assembly. In addition, the rotation transmission device described in U.S. Pat. No. 5,924,510, also assigned to NTN Corporation, and hereby incorporated by reference, describes a device which includes a clutch assembly mounted in the transfer case of a four-wheel drive vehicle that can selectively transmit a driving force. These roller clutch mechanisms, however, often provide for a hard engagement between system components, which may increase wear and decrease performance.
It would be desirable to provide an arrangement which can be used in various applications and includes the advantages of roller clutch mechanism while providing for softer engagement of components or which can be used to delay engagement of components until absolutely necessary. It would be particularly desirable to provide this technology for use with differential assemblies or transfer cases.
A primary object of this invention is therefore to provide a two-way over-running clutch mechanism installed in a system which when energized will provide a limited torque transfer before locking together an input mechanism and output mechanism. This arrangement will provide decreased wear on the components of the system, thereby improving its performance and increasing its service life.
Briefly described, these and other objects are accomplished according to the present invention by providing an arrangement for allowing limited torque to be transferred until a roller clutch mechanism is forced to an engaged position. The present invention includes a roller clutch. A torque generating device is mounted to the roller clutch and includes an actuator for producing an axial force onto a clutch pack. A torque transfer device is disposed between the torque generating device and the roller clutch. The torque transfer device is adapted to receive torque from the torque generating device and to transfer torque to the roller clutch. When a predetermined level of torque is produced by the torque generating device, the torque transfer device moves the roller clutch into an engaged position.